Gear



Sept. i "1, 1928.

A. H.'CANDEE ET AL GEAR Filed July 1, 1925 FIGI INVENTOQS ALLAN H.CANDEE ERNEST WILDHABER.

3 ina u and inversely pro Plasma Sbpt 11, 1192s.

umrso suresn. cninnn AND nnnnsr wrmamnn, or aocnnsrnn, NEW YORK,ASSIGNOBS PATENT OFFICE.

TO GLEASOH NI'W YOBK, A CORPORATION OF NEW YORK.

Application filed my 1,

The present invention relates to gears and particularlyto gears whoseaxesare non-intersecting. One object oi our invention 1s to provide a apair of gears, consisting. of a worm and a crown gear, that shall have1111 roved tooth contact and less frictional loss t an the usual wormgear drive.

. A further objectoi the; invention 1s pro- .10 vide a pair of gears inwhich the dr1 member mayhave a greater dlameter an consequently greaterstrength than in equal ratio bevel gear drives.

Further objects will be apparent herelnafter from the specification andfrom the appended claims.

While we have described and illustrated a particular embodiment of ourinvention, it

is to be understood that the invention is sub- 2 0 ject to furthermodifications within its scope and within the limits-of the claims. 1

In the drawings:

Fig. 1 is a plan view of a pa1r of gears constructed according tothisinvention;

Fig. 2 is a view at right angles to Fig. 1, the parts being shown insection;

Fig. 3 is a side elevation of the pair shown in Fig. 15

Fig. 41s a sectional view corresponding to Fi 3; and i i a F i 5 is adetailed view showing in perspectlve and enlarged a portion of the crowngear member of the new pair. j .The present invention consistsspecifically air of gears one of which is a worm and t e other a crowngear having longitudinally curved teeth, arranged with axes nonintersecting and non-parallel and having threads and teeth respectivelyof opposite hand.

In gear drives where the axes iare-either parallelor intersecting, thepitch diameters of the mating gears must be exactly proportional totheir respective numbers of teeth rtional to the relative velocities.Where t e axis of one of the gears, as the driving gear, is offset fromthe axis of the mating ar, the res ctive pitch diameters are m ependento the gear ratio. 4 Where one of the members is a worm, as in theifesent invention, its pitch diameter may I be c anged at will byaltering its thread- 1925. Serial. No. 40,791.

Iii

ately larger for the same ratio than in bevel gearor similar driveswhere the axes of the mating gears intersect.

The present invention not only provides a stronger driving member witha-larger wearing su face, but also, as-.will be explained furtherhereinafter, provides a pair of gears of superior tooth contact. A

Referring to the drawings, 10- indicates the worm-or driving member ofthe new air, having its axis at'll offset a distance 12 mm the axis 13of the crown gear 14. The thread of the worm 10 is of o posite hand ascompared to the hand of t e teeth of the crown, gear 14. The wormlieswholly on one'side of a'line drawn perpendicular to the axes of the wormand gear.. The peripheral movement of the worm will .be inthedirectionof the arrow 15 and the peripheral movement of the gear in the direction16. The respective peripheral movements,.as' shown,-are at an acuteangle, whereas in ordinary worm drives the peripheral movements are atright angles. This means that there will be less sliding and thereforeless frictional loss in ;a pair of gears constructed according to thepresent invention than in ordinary worm drives.

By taking a section through the worm thread and the gear teeth in a laneparallel to the worm axis and at rig t angles to the gear'axis, we cananalyze the tooth con tact between the members of the new pair of gears.Such a section is shown in Fig. 4'. In this figure, the'sides ofthe-worm thread are indicated at 19 and the sides of the gear teeth at20.- Assuming rotation between the worm and gear to occur at a uniformrate, the sect ons of the worm thread will travel in the direction ofthe projected worm axis -11 at a uniform velocity proportional to thelead of the thread. Since the thread sections will maintain the sameshape during their travel along the line and since the crown gear 14will rotate at a uniform velllh locity proportional to said travel, thecontact between the sides 19 of the worm and the sides 20 of the teethof the crown gear will take place as if the sides 19 of the worm threadwere sides of rack teeth and the sides crown ear then as the mesh of aspur gear and rac it will be understood that the circumference of thepitch-circle of the gear 4 must necessarily equal the distance the racktravels during one revolution of the gear. The lead will equal of coursethe axial pitch 22 of the worm multiplied by the'number of threads orteeth.

If we let R equal the pitch radius of th crown gear, L the lead of theworm, N the number of teeth in the gear and N the num ber of threads inthe worm, we have:

L N R T N Knowing R, the pitch radius of the crown gear, considered as agear rollingon a rack, we can construct the pitch'circle 21 of this.gear. The radiusR is indicated at 24 in Fig. 4. If the mesh ofcrown gearand worm is considered as the mesh of a spur gear and rack, the pitchline of the 'rack must be tangent to the pitch circle of the" gear. Theimaginary pitchlline of=the rack is line 23 parallel to line 11 andtangent to the pitch circle 21 of the gear at the point 25. This point25. is the pitch point for the conjugate profiles of geari and worm andthrough this point passes he instantaneous axis, or axis about which therolling movementof ar and rack takes place at any instant. his axis inthe present case is a line parallel to the axis of the crown gear. It isnoted that the terms pitch circle and pitch oint refer only to theanalogy between t e drive considered and a spur-gear and 'rack drive,

By examining the tooth contact in a series of sections parallel to thesection of Fig. 4, it will be foundthat in the'new gearing the contacton one side of the teeth will extend diagonally across the height of thethread. It will be found also that the tooth surfaces and threadsurfaces are comparatively close fitting. These qualities will enablethegears to carry hea loads and resist wear.

The side vi here the advantage of the improved tooth contact isespecially noticed is theside 27 facing toward the inner end 26 of theworm. The other side 28 of the worm has a contact with the gear similarworm drive. For drives runnin in one rection most of the time, the si e27 will preferabl be made the driving side. This correspon s tosettingthe worm below the center of the crown ear in rear axle drives ofmotor'cars, when e motor rotates in the usual clockwise direction.

As will be seen from Fig. 4 the lead of the worm will be such in a pairconstructed according to the present invention that lines ployed for theworm. Preferably, l1owever,

thesides ofthe worm thread will be made ortions of involute, helicoidalsurfaces. uch surfaces can readily be ground with a flat or planesurfaced grinding wheel. With this structure, in a section taken atright angles to the, worm axis 1L the thread profiles 32 will beinvolutes of a base circle 33..

- In the preferred structure, the outside thread angle of the wormindicated at 34 in Fi 1 will be less than 45 degrees. The outsi e s iralangle isthe complement of the outside: t read angle. The spiral angle ofthe worm thread measured'either at the outside or on; the pitch surfacewill always be greater than the spiral angle of the gear teeth. Thecircumferential pitch of the worm on the outside, indicated at 35, inFig. 2 will also preferably be at least one and one-half times thecircumferential pitch '36- of the crown gear, indicated in Fig. 4; By soproportiomng the thread and teeth of worm and gear, respectively, wehave found a strong and efiicient drive can be secured.

As will-be seenparticularly from Fig. 5, the crown gear is provided withlongitudinally curved teeth whose pressure angle increases continuouslyfrom the inside to the outside of the gear, being larger-at 37 than at38.

' The worm member of the new pair may; be producedin any convenient way,such as by milling or hobbing and may be finished by grinding. The crowngear may be produced by the action of a hob with dimensions cor- Whilewe have illustrated a preferred cmbodiment of our invention it will beunderstood that the invention is capable of further modification withinthe limits of the disclosure and the scope of the appended claims. Thisapplication is intended to cover any variations, uses, or. adaptationsof our invention, following, in general, the princi les of the inventionand ,including such epartures from the present disclosure as come withinknown or customa ractice in the ar artand ma be apphe to the essentiafeatures herein efore set forth and as fall within the limits of theappended claims.

Having thus described our invention, what we claim is:

1. A pair of gears consisting of a cylindrical worm and a crown gear,provided with curved teeth which extend to the outer perrifphery of saidgear, said gear having teeth o posite hand as compared to the thread oft e worm, the spiral angle of said fgear teeth being less than thespiral angle 0 the worm thread.

2. A pair of gears consisting-of a crown gear provided with curved teethwhich ex.

tend to the outer periphery of the gear and a cylindrical worm arrangedwith its axis offset from the axis of the crown gear and extendingbetween the axis of'the crown gear and the toothed portion of said gear,

toothed ortion of said gear, said gear and worm hem of opposite hand andsaid worm havin a t read whose spiral angle is larger than t e spiralangle of the teeth "of the gear. 4. A pa1r of gears consisting of acurved toothcrown gear having teeth which extend to its outer peripheryand a cylindrical worm the peripheral movement of which is at an acuteangleto that of the crown gear,

" said w0rm having a thread whose s iral angle is greater than thespiral angle 0. the teeth of the gear.

5. A pair of gears consisting of a curved tooth crowngearhaving teethwhich extend to its outer periphery, and a c lindric'al worm, theperlpheral movement'o which is at an acute angle to that of the crowngear, said gear and worm being of opposite hand and the spiral angle ofsaid gear teeth being less than the spiral angle of the, worm thread. d

6. A pair of gears consisting of an involute hehooidal worm and a matingcurved.

tooth crown ear.

7. A air 0 gears consi'sing of an involutehelicoi a1 worm and a matingcurved tooth crown gear, arranged Qwith axes nonintersecting andnon-parallel; 8. A air of gears consisting of an mvolute helicoi al wormand a mating crown gear having teeth ofo positehandas compared to thethread of t e worm.

. 9. A pair of gears consisting of an involuite helicoidal worm andmating curved tooth crown gear having teeth of opposite hand as comparedto the thread of the worm.

10. A pair of gears arranged with'axes at right angles andnon-intersecting, consisting of a worm and a mating curved tooth crowngear, having teeth which extend to its outer eriphery, the worm being ofcylindrical orm with the outside thread angle less than 45 degrees, andwith the threads of the worm and teeth of the gear respectively ofopposite hand and with a spiral angle greater than the spiral angle ofthe gear teeth.

11; A pair of gears arranged with axes at right angles annon-intersecting, consisting of-a worm and a matin curved tooth crowngear, having teeth w ich extend to its outer periphery, the-vvorm beingofcylindrical form with the oiitside thread angle less than 45 degrees,and; with the threads of the worm and-the teeth of the gear respectively.of opposite hand, the driving side of the worm facing toward its innerend and the spiral angle of said worm thread being greater than thespiral angle of the gear teeth.

12. A air of gears consisting of a crown gear an a worm extending dianally across the face of said crown gear, 1; e lead of the worm beingsuch that lines drawn respectivelg from the center of the crown gear andt e instantaneous axis to any point of contact between the worm and thecrown gear form an acute angle.

13. A pair of gears consisting of an involute helicoidal worm and amating curved the spiral angle of which is eater than the spiral angleof the teeth 0 the r.'

14. A pair of ears arranged wit axes at right angles annon-intersecting, consistlng of a cylindrical worm and a matin curvedtooth crown gear-having teeth whic extendto its outer periphery, saldgears being so disposed relative y to each other that y the worm lieswholly on, one 'side of a line tooth crown gear, said worm having athread x ion drawn perpendicular the of the two gears. ALLAN H. GANDEE.ERNEST

